The present invention relates to an image forming apparatus, such as a copying machine or a facsimile machine, having a multiple image forming capability to perform a double-sided image transfer or combined image transfer operation, for instance, as well as to a paper return device which is added to an image forming apparatus to give it multiple image forming capability.
In one previous approach to realizing the multiple image forming capability in a copying machine, one side of each sheet of a document is successively copied, individual sheets of copying paper, each carrying a reproduced image on one side, are stacked as if in a stock, and then the other side of each sheet of the document is successively copied. This approach is known as a stock method. In another previous approach known as a non-stock method, two sides of each sheet of a document are copied in succession on two sides of each sheet of copying paper before copying on a succeeding sheet of copying paper.
In one known example of a non-stock type copying machine, a sheet of paper carrying an image reproduced on one side in an image forming section provided inside a main body of the copying machine is ejected through a paper output port, which opens to the outside of the main body of the copying machine, the ejected sheet is transferred to a paper return slot formed in the main body of the copying machine by a reversible paper transport unit which is detachably fitted to the main body, and the sheet reentering from the paper return slot is fed again to the image forming section through a re-feeding path. In this construction, it is possible to provide a paper re-feed mechanism for double-sided copying operation in the form of the reversible paper transport unit which is detachably fitted to the main body of the copying machine. This means that the aforementioned construction makes it possible to provide a double-sided copying mechanism as an optional unit and thereby increase the ease of maintenance.
Today's copying machines are mostly of a type that accommodates paper trays in their main bodies. The majority of this type of copying machines also have manual feed trays for loading sheets of paper to be fed directly from outside their main bodies to permit manual paper feed as is the case with the aforementioned conventional copying machines.
As will be noted from the above discussion, a conventional copying machine having the aforementioned construction usually has two paper paths for feeding paper to an image forming section from outside a main body of the copying machine. These are a re-feeding path for feeding the paper transferred by a reversible paper transport unit and a manual feeding path for feeding individual sheets of paper loaded on a manual feed tray. A problem of this conventional structure is that the provision of more than one paper path for similar use leads to an inefficient use of available space and an increase in equipment cost.